Method of drawing



Maw-19, 1942. w. ERNST 2,283,356

METHOD OF DRAWING Original Filed March 27, 1939 z'sheets-sneei 1 Im/cntor WALTER ERNST v Attomq's May 19, ERNST amnion 0F DRAWING 0rigin l Filec l llarch 27, 1939 2 Sheets-Sheet 2 I Q Patented May 19, 1942 Ms'rnon or naawn'vo Walter Ernst, Mount Gilead, Ohio, assignor to The Hydraulic Development Corporation, Inc.,

Wilmington, D el., a corporation of Delaware Original application March 2'7, 1939, Serial No. 264,311. Divided and this application August 28, 1939, Serial No. 292,271

3 Claims.

This invention-relates to presses, and in particular, to hydraulic presses having clamping mechanism associated with drawing mechanism.

One object of this invention is to provide a hydraulic press having a drawing plunger and a clamping plunger, means being provided for releasing the pressure from the clamping plunger during the retraction stroke of the drawing.

plunger, together with means for preventing the release of this pressure during the drawing stroke.

Another object is to provide a hydraulic press having a drawing plunger and a clamping plunger, togetherwith means responsive to the reversal of pressure fluid for retracting the drawing plunger in order to release the pressure in the clamping plunger.

Another object is to provide a hydraulic press having a drawing plunger and a clamping plung .er, together with a valve shifted in response to the reversal of the drawing'plunger by pressure fluid supplied for retracting the latter so that the valve for releasing the pressure from the clamping plunger is automatically actuated by the pressure condition existing in the drawing plunger circuit without the necessity for the provision of linkages or other mechanism interconnecting the drawing plunger with the valve.

Another object is to provide a method of producing drawn articles, residing in clamping the article at its periphery by hydraulically operated means while performing the drawing operation, and thereafter releasing the pressure from the hydraulic clamping means in response to the reception of pressure for reversing the drawing operation.

This application is a division of my application Serial No. 264,311, filed March 27, 1939, which has resulted in Patent No. 2,252,881, Aug. 19, 1941.

In the drawings:

Figure 1 is a diagrammatic view, partly in section, showing the working elements of a hydraulic drawing press circuit according to one embodinient of this invention, wherein a reversing valve controls the distribution of fluid to the drawing plunger.

Figure 2 is a diagrammatic view of a modification of the circuit. shown in Figure 1, wherein a reversible pump is employed for reversely distributing pressure fluid to the drawing plunger to advance and retract the latter.

General arrangement In general, the drawing press of this invention consists of a drawing plunger and a plurality of clamping plungers having relief valves associated therewith for release of the pressure fluid therein at predetermined pressures, thereby enabling a predetermined clamping pressure to be exerted on the blank. The relief valves may beset at different loadings so as to provide diiferent clamping pressures at different points upon the blank. Check valves are employed to prevent the interflow of fluid between the various clamping cylinders, thereby preventing equalization of clamping pressures. The hydraulic circuit also includes a two-way valve connected to the clamping cylinders, and operated in response to the admission of pressure fluid into the retraction circuit of the drawing plunger. By this arrangement it is impossible to release the clamping pressure until the retraction stroke of the drawing plunger has been started.

Hitherto, the provision of a platen-operate valve for releasing the pressure from the clamping cylinders has required complex mechanism,

, such as linkages actuated by the platen for shifting the valve. This, in turn, has required an individual adjustment of this mechanism to be made every time the dies are, changed, and has always created the danger of erroneous adjustment whereby the valve would not be operated at all, or would be operated at the wrong position.

According to the present invention, however, the platen-operated mechanism for shifting the valve is entirely eliminated, and instead the valve is shifted by pressure fluid applied thereto when pressure iluid is admitted into the retraction circuit of the drawing plunger. This construction simplifies the external appearance of the press, results in economy of manufacture, avoids the possibility of maladjustment and savesthe time hitherto required for adjusting the platen-operated mechanism to suit various dies. Accord ing to the present invention also the clamping pressure releasing valve is preferably mounted inside the oil reservoir so that leakage is of no.

consequence.

Press circuit employing pump with reversing valve Referring to the drawings in detail, Figure 1 shows diagrammatically a hydraulic metal drawing press having a base member it! connected to a top member H by tie rods H, the latter being cut oil for simplicity of showing. Mounted in the base member it is a drawing die it having a die cavity l5 for receiving the blank it. The die it is received within a bore it in the base member 6. The drawing press of the present invention may utilize either flat blanks or blanks which have already been subjected to one or more drawing operations. In Figures 1 and 2 the blank I6 is illustrated as having been previously subjected to one drawing operation and in position for another drawing operation, which will elongate it and cause it to be drawn downwardly into the die cavity l5.

Associated withthe top member H of the press is a surge tank l6 or oil reservoir for containing the working fluid by which the press is actuated. Also associated with the top member II is a main cylinder or drawing cylinder 20, having a bore 2| reciprocably receiving the double-acting main plunger or drawing plunger 22 having a piston head 23 thereon. The cylinder 26 is provided with upper and lower ports 24 and 25 on opposite sides of the piston head 23, and adapted by means of pipes 26 and 21 to supply pressure fluid to advance or retract the drawing plunger 22. The delivery of pressure fluid to the main cylinder 26 and the exhaustion of fluid therefrom are controlled by a four-way valve 26. This valve 28 is of any suitable type known to those-skilled in the art, and its details form no part of the present invention.

Leading to the four-way valve 28 is a pressure line 29, connected at its opposite end to a hydraulic pump 36. An exhaust line 3| leads from the four-way valve 26 to the interior of the surge tank IS. The pump 36 is also provided with a suction line 32, likewise leading into the interior of the surge tank IQ for supplyin fluid. to the pump. The main or drawing cylinder 26 is provided, near its lower end, with a packing ring 33 having a packing 34 associated therewith and adapted to be compressed by a gland 35 in such a manner as to prevent leakage around the drawing plunger 22. I

Mounted upon the lower end of the drawing plunger 22 is a platen 36 containing clamping cylinders 31, having clamping plungers 38 reciprocable therein. Each clamping cylinder 31 is provided with a packing 39 surrounding the clamping plunger 38, and compressed by a gland 46 for the prevention of leakage. Mounted upon the platen 36 is a drawing die member or punch 4|, cooperating with the drawing die I4 and having a nose portion 42 approximately corresponding to the die cavity l5. The punch 4| is adapted to pass through an aperture 43 in a clamping member 44, the latter being secured to the outer ends of the clamping plungers 38.

The clamping cylinders 31 are provided with passages 41 connected to the bores 49 of tubular plungers 48, mounted upon the upper side of the platen 36. The hollow plungers 48 pass through glands 50 and packings into cylinders 52 arranged on the press top member H and within the surge tank l9. From each cylinder 52 the line 53 leads through the check valve 54 to the interior of the surge tank l9. Each check valve 54 opens in the direction of the cylinder 52 so that the latter may draw in fluid upon the descent of the hollow plungers 48. The check valves 54, however, close and prevent the discharge of fluid upon the ascent of the plungers 48.

From each cylinder 52 a T-shaped line 55 leads also to a safety valve 56 and a pressure relief valve 51. The safety valve 56 is merely provided as an additional safety feature in the event of a jamming or other failure of the relief valve 51. The safety valve 56, however, is set to release pressure at a higher pressure than the relief valve 51, hence, does not become operative unless the relief valve 51 fails to release fluid in response to the accumulation of a dangerous pressure within the corresponding clamping cylinder 31. Each clamping cylinder 31 is provided with its own pressure relief valve 51 and safety valve 56 so that a diflferent pressure release point may be provided for each clamping cylinder 31, if desired. This, in turn, enables diflferent clamping pressures to be exerted upon different portions of the periphery of the blank |6, a feature which is useful in certain classes of drawing work.

The valves 56 and 51 both discharge into the discharge line 56, leading to the interior of the surge tank I6. A pressure gauge 56 is connected to each line 65 to indicate pressure existing in the associated clamping cylinder 31. Extending from each clamping cylinder 52 is a line 6| having therein a check valve 62, opening in a direction away from its associated clamping cylinder 52 and toward a common line 63 connected thereto. The line 63 leads to a two-way valve 16, having a cylindrical bore 1| containing a valve member 12 with valve heads 16 and 14. The opposite ends of-the cylinder bore 1| are provided with ports 15 and 16. A branch line 11 leads from the line 26 to the port 16, whereas a branch line 18 leads from the line 21 to the port 15. The cylinder bore 1| likewise contains a discharge port 16, opening directly into the interior of the surge tank l6, and an additional port 86 to which the line 63 is connected. The end portions of the valve bore 1| immediately adjacent the ports 15 and 16 serve as pilot chambers or valve-actuating chambers for shifting the valve member 12 in response to the reception of pressure fluid either. along the line 16 or 11 from the line 21 or 26, respectively.

The platen 36 is provided with bores 6| adapted to receive rods 82, the lower ends of which are secured to the clamping platen 44 and the upper ends of which are externally threaded, as at 83, and provided with nuts 64 threaded thereon. The upper ends of the rods 62 are likewise provided with internal threaded bores 85, carrying the threaded rods 86. This construction provides means for stripping the workpiece from the punch 4| when the rods 86 encounter the press top member upon the return stroke .of the main plunger 22. The construction permits this ejection or knock-out point to be accurately adjusted for each difierent type of workpiece.

Operation In the operation of the circuit shown in Figure 1 the pump 36 is placed in operation, and the valve 28 is shifted by means of its operating lever 81 so that pressure fluid is admitted to the line 26, and thence to the upper part of the main cylinder 26 above the piston head 23. At the same time fluid is exhausted from beneath the piston head 23, through the line 21, and is discharged through the valve 26 to the line 3|, and thence into the surge tank l9. When this occurs pressure fluid likewise passes through the line 11 and port 16, into the left-hand end of the cylinder bore 1|, any fluid in the right-hand end of the cylinder bore 1| being discharged through the port 15 and line 18 by way of the valve 28 and line 3|, into the surge tank l9.

Under the influence of the pressure in the line 11, the valve member 12 is pushed to the right so that the valve head 13 comes to rest between inder bore II, and cannot escape through the port I9. Ordinarily, a surge valve is provided in thetop of the main cylinder 20 to admit fluid freely upon the downward stroke of the drawing plunger 22, thereby accelerating the gravitational descent of the platen 38. This surge valve is omitted for simplicity of disclosure, and its use is well known to those skilled in the art.

As the main plunger 22 moves downwardly it carries with it .the platen 3i and the clamping assembly, which includes the clamping platen 44, the clamping plungers 38 and the tubular plungers 48. The suction thereby created in the cylinders 52 opens the check valves 54 and causes fluid to be drawn from the surge tank I0, into the cylinders 52. When the clamping member or clamping platen 44 has descended to a point where it engages the workpiece I6 it halts. The platen 36, however, continues to advance and moves the punch 4! into engagement with the workpiece It. By reason of the relative motion thus created between the halted clamping plungers 38 and the moving clamping cylinders 37,

fluid from the cylinders 52 the instant that pressure fluid is admitted to the retraction side of the main plunger-22. There is thus no necessity for any leakage or any attention on the part of fluid is displaced by the plungers 30 from the cylinders 31. The displaced fluid passes through sectional area. of the clamping plungers 38 is greater than the cross sectional area of the tubular plungers 48, however, more fluid is discharged from the clamping cylinders 31 into the cylinders 52 than there is room for. This results in pressure being built up in the cylinders 31 and 52, and this pressure acts against the heads of the plungers-4B and 38 to force the clamping member or clamping platen M firmly into engagement with the periphery of the workpiece I6.

When pressure in this clamping system exceeds the setting of the relief valves 51, the latter open and permit the excess fluid to be discharged through the lines 58, into the surge tank I9. The check valves 56 prevent the escape of fluid through the lines 53, and the closed position of the valve I0 prevents the discharge a of fluid from the-line 63 since the valve head 13 now stands between the'ports 80 and I9. Consequently, the clamping platen i4 grips the periphery of the workpiece or blank It while the punch M is urged downwardly by the main platen 36, thereby performing the drawing operation upon the workpiece I6. When the required operation has been completed, the valve lever 87 is manipulated-to shift' the four-way valve 20 so that pressure fluid is discharged from the pump 30, into the line 21 leading to the retraction side of the main plunger 22. At the same time the space above the piston head 23 is open to exhaustthrough the line 26, the four-way valve 28 and the exhaust line 3| leading to the surge tank I9. Under these conditions the main plunger 22 and main platen 36 move upward.

The admission of pressure fluid to the retraction line 21 also admits pressure fluid to the line 78, this fluid entering the port I5 at the righthand end of the cylinder bore II in the valve 70, and shifts the valve member I2 to the left into the position shown in Figure 1. As the tubular plungers 48 move upwardly, therefore, the fluid displaced from the cylinders 02 escapes through the lines SI, the check valves 62, the line 63, the port 80, the valve bore Hand the port 79, into the surge tank I9. This enables the tubular plungers 48 to be freely retracted along with the main plunger 22 and main platen 36. In the arrangement of Figure 1, therefore, the valve '80 is automatically shifted to permit the escape of the operator for shifting the valve 10 to permit the escape of this fluid.

Modified drawing press circuit employing reversible pump The'modlfled arrangement shown in Figure 2 I is similar to the arrangement shown'in Figure l, as regards the general construction of the press itself, and likewise is provided with similar relief and safety valves 51 and 56 for the cylinders 52. The common line 83, however, is connected to a valve 90, of a slightly different construction from the two-way valve 10 of Figure l, but serving essentially the same purpose. The valve 90 is provided with a valve bore 8|, containing a valve member 82 having heads 93 and 94. The valve member 92 carries a third valve head 95, reciprocable in an independent bore 96 having ports 07 and 98 at the opposite ends thereof. The valve bore Si is provided with ports 93 and 100, similar in arrangement and purpose to the ports I9 and of the valve 10 in Figure l. The line 03 is connected, in Figure 2, to the port I00 and the port 99 opens directly into the interior of the surge tank I9.

In the circuit of Figure 2 the pressure fluid is supplied selectively to the line 21 or 26 from a reversible variable delivery pump IN. The latter is provided with a flow-control member or shift ring (not shown), familiar to those skilled in the art, and shifted to and fro by a servomotor I02 in order to vary the direction .and amount of the fluid delivered from the pump IOI. Mounted on the opposite side of the pump IOI from the servomotor I02 is a safety centering device I08 for shifting the flow-control member of the pump "II to its neutral position in the event of a power failure to the motor driving the pump WI. The details of the servomotor I02 and safety centering device I03 form no part of the present invention, and are disclosed in the copending application of Walter Ernst, Ser. No.

170,250, filed October 21, 1937.

The servomotor I02 contains a servopiston connected to the pump flow-control member, and actuated in opposite directions in response to the shifting of the servomotor control valve" member ally mounted upon a fulcrum I It, supported upon the press head II, or any other stationary part of the press. One end of the rocker arm H3 is provided with a rounded yoke portion II5 engaging a collar IIB upon the press control rod III;

The latter is reciprocably supported upon the press, such as in the bore H8 on the press head II, and by the bore H9 in the bracket I20 secured to the press bed I0.

' The platen 36 carries a platen arm I2I enageable with an adjustable collar I22 upon the control rod '8. The opposite end of the rocker arm 8 from theyoke portion H5 ispivotally connected to a rod I23, leading to the armature I24 of a solenoid I25. The energization of the solenoid I25, acting through the above-mentioned linkage, pushes the servomotor control valve member I04 to the right, whereas a spring within the servomotor I02 urges it to the left when the solenoid I25 is deenergized. When the platen 36 reaches its retracted position, the arm I2I lifts the control rod I I1, and the collar I I6 thereon shifts the rocker arm H3 in such a manner as to move the servomotor control valve member I04 to the right into its neutral position, thereby placing the flow-control member of the pump IOI in its neutral position, and reducing the delivery of the pump IN to zero. This halts the platen 36 in its retracted position.

The motor which drives the variable delivery pump IOI' also drives a pilot pump I26, preferably from the same shaft. The pilot pump I26 delivers pressure fluid through the line I21 to the servomotor I02, thereby operating the servomotor, and withdraws fluid from the surge tank I9 by way of the suction line I28. The line I21 thus serves as a pilot pressure line, and contains a relief valve I29 having a. discharge line I30 discharging into the surge tank I9. The servomotor I02 is also provided with an exhaust line I3I, similarly discharging into the surge tank I9. A pressure line I32 leads from the servomotor I02 to the end port 91 ofthe bore 96 within the valve 90. The main cylinder 20 is provided with a bore I33 in the head thereof, and serves to receive 'a surge valve I34 connected by the line I35 to the line I36, which in turn, is connected to the.

line 21 leading to the retraction side of the main plunger 22. The surge valve I34 is of the type disclosed in the patent to Walter Ernst, No. 1,892,568, issued December 27, 1932.

The line I36'is provided with a branch line I31 having a check valve I38, opening toward the line I36. The line I36 is additionally provided with a pressure relief valve I39, and is connected at its end to a main cylinder release and by-pass valve I40, having a line I4I leading to the port I42 in the head of the main cylinder A branch line I43 likewise leads from the valve I40 to theline HI, and a second branch line I44 terminates in a pressure relief valve I45. Thedetails of the main cylinder release and by-pass valve I40 form no part of the pres- -ent invention, and are disclosed in the patent to Walter Ernst, No. 1,956,758, issued May 1,1934. Running from the line I36 is a branch line I46 leading to the port 98 in the valve 90.

In order to provide a variable pressure control to alter the energization of the solenoid I and to automatically reverse the main plunger 22 at the attainment of a predetermined pressure during its working stroke, there is provided a tonnage control device I41 having a line I48 con-- nected to the port I49 in the head of the main cylinder 20, and likewise having an exhaust line I50 connected to the interior of the surge tank I9. The tonnage control device I41 consists of a spring-loaded hydraulic plunger reciprocable in a chamber connected to the line I48, and

movable to actuate an electric switch in circuit with the solenoid I25 when the pressure in the line I48 overcomes the force of the loading spring, at which time the plunger uncovers a port leadingito the line I50, and the excess pressure fluid discharges into the line I50. The loading of the spring within the tonnage control device I41 is regulated by the hand wheel I5I so as to vary the pressure at which the switch therein-becomes operative to alter the energization of the solenoid I25. The tonnage control device I41 is therefore, in principle, a pressure-responsive electric switch, and its details are well known to those skilled in the art and form no part of the present invention.

Operation of modified press circuit In the operation of the modified press circuit shown in Figure 2, the pumps IOI and I26 are started in operation, preferably by energization of the solenoid I25, or manually by shifting the press control rod II1 downwardly by a hand lever (not shown). The resulting motion of the servomotor control valve member I04 shifts the flow-control member or shift ring of the pump IOI so as to place the latter upon stroke to discharge pressure fluid into the line 26 while withdrawing pressure fluid from the line 21. The main plunger 22 descends, as described in connection with Figure l, and its gravitational descent is accelerated by the free admission of fluid from the surge tank I9, through the surge valve I34, into the upper end of the main cylinder 20.

At the same time, when the pilot pump I26 delivers pressure fluid to the servomotor I02 to place the pump IOI upon stroke to deliver pressure fluid into the line 26 and advance the main plunger 22, pilot pressure fluid also passes out of the servomotor I 02, through the line I32, into the end chamber 96 of the valve 90, acting against'the vave head 95 and shifting it to the left. This action shifts the valve head 94 into a position between the ports I00 and 99, and blocks the escape of fluid from the line 63, through the valve 90. Since the pilot pressure fluid remains at practically constant pressure, it can be depended upon to hold the valve in its closed position during the power or working stroke of the main plunger 22. The valve 90 in Figure 2 is operated by pilot pressure in this manner rather than connected to the line 26 leading to pressure from the cylinders 52 and 31. After the clamping member 44 engages the workpiece I6, the operation of the clamping apparatus 38, 31, 48, 52, etc., is as described in connection with the circuit of Figure 1.

When the drawing operation has proceeded to a point where the tonnage control device I41 deenergizes the solenoid I25 to reverse the delivery of the pump IOI, the latter then discharges pressure fluid into the retraction line 21 and withdraws fluid from the advancing line 26. The main plunger 22 then rises, but a portion of the pressure passes through the lines I36 and I46, into the left-hand end of the valve bore 96. This pressure forces the valve head and the valve member 92 to the right, into the position shown in Figure 2. At this time the line I32 is connected to the servomotor exhaust line HM, and releases any fluid in the right-hand end of the valve bore 96. The consequent shifting of the valve head 94 vto the position shown in Figure 2 opens communication between the ports99 and I00, and permits fluid to escape from the cylinders 52 and 31 of the clamping circuit analogous to the manner described in connection with Figure 1. The clamping platen 4G is, therefore, permitted to be retracted along with the main plate 36 and main plunger 22.

When the platen 35 nears the end of its retrac tion stroke, the collar i2: on the control rod ill is lifted by the platen arm I! l shifting the servomotor control valve member I to its neutral position, and placing the flow-control member 01' the variable delivery pump I in its neutral or zero delivery position. This brings the platen 36 to a halt at the top of its retraction stroke.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claimsand the 111-. vention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A method of drawing workpieces in presses having a drawing vmill-Eider for operation of a drawing die, and a clamping cylinder, which comprises the step of admitting pressure fluid into the drawing cylinder and concommitantly therehaving a drawing die and a clamping cylinder, which includes the steps'of (a) closing an outlet from-and thus preventing the escape of fluid from the clamping cylinder and simultaneously subjecting said die and clamping cylinder to hydraulic pressure to-initiate the advancing or drawing movement thereof, (b) clamping the work piece hydraulically while performing the drawing operation, and (c) reversing said hydraulic pressure on said die at the end of the drawing operation to initiate, the retraction of said die, and simultaneously'therewith applying said last mentioned pressure instantly to-open the outlet from and thus release the fluid entrapped in said clamping cylinder;

3. A method of drawing workpieces in presses having a drawing die and a clamping cylinder,

with applying pressure fiuid independent of said first-named pressure fluid for closing the escape of fluid from the clamping cylinder, clamping the work piece hydraulically while performing the drawing operation, and relieving the hydraulic pressure by permitting the escape of fluid from the clamping cylinders instantly in response to the application of hydraulic pressure to reverse gliie drawing operation and retract the drawing e. I 2. A method of drawing workpieces in presses stripping the work' piece fromthe drawing die at a position between its end positions. I

WALTER ERNST. 

